The present invention relates to a method and apparatus for the control of air conditioning systems used to cool the passenger compartments of over-the-road vehicles, such as trucks and automobiles. The invention is concerned with air conditioning systems including a cooling-medium compressor which is driven by the vehicle engine, such that during periods of maximum power requirements for the engine (e.g., acceleration) the air conditioning system is automatically turned off (i.e., taken off line), but during periods of normal or less than normal power requirements (i.e., cruising, idling and deceleration) the air conditioning system is operating to control the vehicle passenger compartment within the desired comfort range of temperature.
Previous methods for using and controlling an automotive air conditioning system include the following systems:
(1) The air conditioner is left on at all times and passenger compartment temperature is controlled by manual adjustment of the reheat system; PA1 (2) The air conditioner is left on at all times and the passenger compartment temperature is controlled by thermostatic control of the reheat system; PA1 (3) A passenger compartment thermostat control is provided for the air conditioner compressor on/off control as a function of passenger compartment or conditioned air temperature. PA1 (1) during acceleration and cruising, the air conditioning system is automatically controlled by thermostat and left off if the passenger compartment temperature is within the desired comfort limits; PA1 (2) during cruising, the air conditioning system is automatically activated by thermostat if the passenger compartment temperature is higher than the desired comfort limits; PA1 (3) during deceleration and idle, the air conditioning system is automatically activated by the mercury switch (after a short delay, e.g., about 2 to 5seconds), when the passenger compartment temperature is higher than the desired comfort limits or within the high side limits of the comfort range; PA1 (4) during deceleration and idle, the air conditioning system is automatically turned off by thermostat if the passenger compartment is lower than the desired comfort limits: PA1 (5) in one preferred embodiment, the control system utilizes the following monofunctional logic control that affords added safety at critical periods: during hard acceleration and/or increased power requirement periods (such as passing, pulling out into traffic, high climbing, etc.) the high acceleration and/or increased power requirement are sensed by an accelerometer, which senses changes in apparent inertia, and the air conditioning system is automatically turned off line and stays off regardless of the passenger compartment temperature to allow additional drive line power needed from the vehicle engine. PA1 (6) in a second preferred embodiment the control system utilizes a multifunctional logic, one or more devices sense acceleration/cruise/deceleration/idle/orientation and interpret this acceleration/cruise/deceleration/idle/orientation to control the air conditioning system in the appropriate manner, as previously mentioned. The device is preferably an accelerometer, which senses changes in inertia, speed and/or orientation of the vehicle and most preferably is a mercury switch. PA1 (7) if the vehicle brake remains activated for a specified of commands from the accelerometer, because the vehicle will most likely be at rest or decelerating and its orientation (level) might cause erroneous commands from the accelerometer, and because the engine idle mode will be imminent. PA1 (1) the work of cooling may be varied by a variable speed drive on the compressor; PA1 (2) the work of cooling may be varied by varying the amount of slip in any type of compressor clutch; PA1 (3) the cooling work may be varied by proportional means of unloading and loading the compressor, or on/off valving of the refrigerant lines; PA1 (4) the cooling work may be varied by any other known means of loading or unloading the compressor; PA1 (6) the cooling work may be varied in the air conditioning system by varying the amount of air available for compression, by varying the compression ratio, or by varying the speed of the compressor. PA1 (7) the cooling work may be varied in the conventional air conditioning system by varying the amount of refrigerant available for compression by varying the compression ratio or by varying the speed of the compressor. PA1 (1) reduced fuel consumption with the air conditioning system on because most of the energy required for the work of cooling is provided from the vehicle's kinetic energy during periods of lower power requirements, e.g., deceleration and cruise, rather than solely from chemical energy (fuel) consumption; PA1 (2) improved operation and safety for vehicles with relatively low power output engines (i.e., compact and sub-compact automobiles) because more available engine power is provided to the drive train during periods of acceleration or hill climbing because the compressor is off line and not utilizing power. This advantage would be primarily important to vehicles with small engines, that in many cases do not provide sufficient power for good acceleration (hence safe operation in passing, high climbing or pulling out into traffic) when the air conditioning system is on. Many drivers of vehicles with small engines are habitually distracted when they turn off their air conditioning systems when added power is required for passing or pulling into traffic; hill climbing, etc.; PA1 (3) improved passenger compartment temperature control because the passenger compartment temperature sensor would provide space comfort more efficiently (as a function of fuel consumption) by controlling compartment temperature with on/off operation of the compressor rather than allowing the compressor to run continuously and relying on a constant reheat of cooled air as is used in most conventional vehicle air conditioning systems.
There are a number of disadvantages inherent in these prior art methods, among which are: decreased fuel economy with the air conditioning system left on; decreased power, acceleration and safety with the air conditioning system on (This is especially important for cars with small engines that need all available engine power for maximum acceleration situations, such as passing, pulling into traffic, and hill climbing where more power is needed); and inefficient temperature control by blending hot air (reheat) manually or automatically (inefficient temperature control) by switching the compressor of the air conditioning system on and off by means consisting solely of a thermostatic control.
Many automobiles are equipped with an air-conditioning system. The compressor of the air conditioner imposes a relatively constant drag on the engine and the installation of the air conditioner has, in past years, often been limited, as a practical matter, to automobiles having a relatively high power output engine and large displacement, to assure maximum power in situations where quick acceleration is needed for safety considerations. Even with the newer, smaller and more efficient air conditioning systems used with smaller engines, fuel economy and safety are limited when the air conditioning system is on, as well as power being limited during periods of maximum power requirements for the engine (acceleration situations).